Preparation of di-lithio (perfluoroalkylethylsilyl) neocarboranes

ABSTRACT

THIS INVENTION RELATES TO A PROCESS FOR THE PREPARATION OF DI-LITHIO (PERFLUOROALKYLETHYLSILYL) NEOCARBORANES BY REACTING DILITHIONEOCARBORANE WITH A CYCLIC TRISILOXANE.

United States Patent US. Cl. 260-4482 4 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a process for the preparation of di-lithio (perfluoroalkylethylsilyl)neocarboranes by reacting dilithioneocarborane with a cyclic trisiloxane.

Silicon-containing organoboron polymers have gained importance because of their thermal and oxidative stability. The siloxy-carboranyl polymers are generally prepared by the ferric chloride catalyzed reaction of certain bis(halosilyl)-neocarboranes with certain bis(alkoxysilyl) neocarboranes. Disiloxanyl neocarboranes can also be reacted in this manner.

The silyl and disiloxanyl neocarborane precursors are prepared by reaction of dilithioneocarborane with halosilanes or halodisiloxanes. Examples of such preparations are disclosed in US. Pats. 3,388,090 and 3,397,221. These preparations rely upon the reaction of lithium and chlorine to form the ESi--CB H C-SE bonding in the precursors to siloxy-carboranyl polymers. By the practice of the invention, there is provided another reaction route to the production of such useful intermediates.

The process of the present invention provides a method of preparing silicon-containing organoboron compounds of the formula trisiloxane of the formula (RR SiO) in which R and Rf are as defined above in the presence of an inert organic solvent.

Thus, R can be any alkyl radical, straight or branched chain, for example, ethyl, i-propyl, n-butyl, octyl or dodecyl radicals. The perfluoroalkyl moiety otR can be CF C 1 C F and so on, through the -C F and -C F radicals.

The dilithioneocarborane reactant is prepared by reacting m-carborane (i.e. neocarborane) with a lithium alkyl compound, such as n-butyllithium, by means of slow addition of the lithium alkyl to neocarborane in a suitable solvent, such as the lower dialkyl ethers. The cyclic trisiloxane starting materials are well-known compounds. The dilithioneocarborane-cyclic trisiloxane reaction proceeds at temperatures in the range of from about 0 C. to about 100 C. Generally, the reaction is carried out at from 29 C. to 30 C. The pressure employed in the reaction 'can be varied, although it is most convenient to utilize atmospheric pressure. It is necessary to react at least /3 mole of the trimer per mole of dilithioneocarborane in order to obtain the desired disubstitution. The time necessary for completion of the reaction varies with the reaction temperature. At room temperature equilibrium is attained in less than one hour.

The reaction is carried out in the presence of an inert organic solvent. Suitable solvents include dialkyl ethers, for example, diethyl ether, methyl ethyl ether, diisopropyl ether, di-n-propyl ether, ethyl-n-butyl ether, ethylene glycol dimethyl ether, dioxane and tetrahydrofuran and mixed solvents, such as diethylether-pentane, di-n-propyl ether-heptane, dioxanehexane, etc.

The products of this process are a mixture of the lithium cndblocked bis(silyl)neocarboranes in which the number of siloxy units in the individual compound varies. Depending upon the molar ratio of reactants, the product will contain various proportions of compounds in which n equals 0, 1, 2 or 3 and m equals 0, 1, 2 or 3.

These lithium cndblocked bis(silyl)neocarboranes are useful intermediates in the preparation of siloxy-carboranyl polymers in which the silicon atom contains a perfluoroalkylethyl substituent. The products are hydrolyzed to obtain diols which are then condensed in the presence of an acid catalyst to obtain polymeric fluids and elastomcrs which have utility as heat-stable fluids and sealants. The use of the products of the instant process as intermediates is illustrated in the examples.

EXAMPLE 1 A typical preparation of C,C'-dilithioneocarborane involved the addition of several grams of activated charcoal to a solution containing 1 lb. of ether and 195 g. (1.34 moles) of neocarborane. The mixture was then filtered to remove impurities. Three moles of butyllithium were added slowly with rapid stirring. After stirring for 2-3 hours at room temperature, the material Was then filtered through a nitrogen-filled, fritted glass, closed funnel. The solids were washed twice with 200 ml. portions of hexane. The semi-dry solid was then added to 1-2 lbs. of ether which formed a slurry. The solid LiCB H CLi can be exposed to or transferred to a flask through high humidity air without excessive danger of fire.

EXAMPLE 2 A dilithioneocarborane slurry was made starting with 29 grams (0.2 mole) of m-carborane. To the slurry was added 62 grams (0.13 mole) of 1,3,5-tris(3,3,3-trifluoropropyl)-1,3,S-trimethylcyclotrisiloxane dissolved in 100 milliliters of ether. The mixture was stirred for two days to obtain a mixture of compounds of the general formula Me represents (CH and P represents (CH CH CF n and m both equaling from 0 to 3.

grams (0.5 mole) of (3,3,3-trifluoropropyl)-methyldichlorosilane were added to the above reaction product at room temperature over a 30 minute period. The mixture was then filtered and distilled. A number of compounds were isolated having the general structure Cl(SiP MeO) SiP MeCB I-I CP MeSi(OP MeSD Cl where n=0, m-=1, (19%); 11:1, m=1 (27%); n=2, m=1 (9%).

G.l.p.c. comparison analysis with known compounds also indicated the presence of compounds having the same general structure where n\=0, m=0 (9%) and where n=2, m=2 (5%),

in the intermediate fractions and residues. The above yields are approximations based on g.l.p.c. analysis. The overall yield was 70%. The structure, distilled yield (97% pure) and properties of the compounds isolated are listed below.

21:1, m (16%).Boiling point l50-l55/0.3 mm. Hg. The structure was confirmed by H N.M.R. Chlorine analysis was 10.48% (theory 10.91%).

11:1, "i=1; (16%).Boiling point l60l66/0.3 mm. Hg. The structure was confirmed by infrared and H N.M.R. analysis. Chlorine analysis was 7.60% (theory 8.79%).

"=1, "i=2; (8.5%).Boiling point l28/0.l mm. Hg. The structure was confirmed by infrared and H N.M.R. spectroscopy. Chlorine analysis was 7.44% (theory 7.37%).

EXAMPLE 3 A gram (0.025 mole), portion of CH3 CH3 CH2 CH2 ClS iOSiCBioILgC-SiO-SiCl, a... t... t... a... on: CH2 CH2 CH2 CF: CFs CF14 CFa prepared as described in Example 2 was dissolved in milliliters of acetone. To this was added 18 grams (1.0 mole) of water in 25 milliliters of acetone. After stirring, water and ether were added and the organic layer was washed with water until neutral. The water was removed and benzene was added and the mixture refluxed to remove the last traces of water. Evaporation of the solvents under reduced pressure left a residue product of 14.5 grams (76% yield) of the bis(hydroxydisiloxanyl)- neocarborane, which was then condensed in the presence of tetrafluorosulfonic acid to obtain a polymer of the formula which was a highly viscous, clear fluid.

EXAMPLE 4 A C,C-dilithiocarborane ether slurry was made by utilizing 195 grams of m-carborane in accordance with the method described in Example 1. This slurry was added to 312 grams of 3,3,3-trifiuoropropylmethylsiloxane cyclic trimer which was dissolved in 150 milliliters of ether. After stirring for several hours, 360 grams (1 mole percent) of 3,3,3-trifluoropropylmethyldichlorosilane were added to the reaction mixture. The material was then filtered and hydrolyzed in water. The hydrolyzate was stripped at 225 C./0.3 mm. Hg to remove impurities and volatile material. The hydrolyzate was partially condensed 4 during the stripping operation to give a prepolymer having the general structure:

out r out w on. w on; 1 iiOS i CBmHmCS iOSji0H.' (2:11. on. (III-I2 on;

CH2 CH3 CH2 CH2 CF: CFJ 0-2 LCF; 0-2 CF:

A portion of the prepolymer was mixed with a small amount of methyltriacetoxysilane and cured to an elastomer.

When a condensation catalyst, such as sulfonic acid, is added to the prepolymer and the mixture is further heated, at high molecular weight polymer of the various carborane-siloxy units is obtained.

That which is claimed is:

1. A method of preparing neocarboranes of the for- R is a fi-perfiuoroalkyl radical containing from 3-12 inclusive carbon atoms;

R is an alkyl radical containing from 1-12 inclusive carbon atoms or a R radical;

n is an integer having a value of from 0 to 3 inclusive and m is an integer having a value of from 0 to 3 inclusive;

comprising reacting dilithioneocarborane with a. cyclic trisiloxane of the formula UNITED STATES PATENTS 3,388,090 6/1968 Heying et a1. 260448.2XR 3,388,093 6/1968 Heying et a1. 260-448.2X 3,397,221 8/1968 Papetti 260448.2(N) 3,450,739 6/1969 Heying et al 260448.2X

TOBIAS E. LEVOW, Primary Examiner P. F. SHAVER, Assistant Examiner U.S. Cl- X-R. 26 0l6 5 

